Text and graphic separation method and text enhancement method

ABSTRACT

The present invention provides a text and graphic separation method and a text enhancement method. The text and graphic separation method is used for separating texts and graphics of an image and comprises coarse classification and advanced classification. The method of the present invention also adjusts the luminance of the text to enhance the text image according to the separation result.

FIELD OF THE INVENTION

The present invention relates to a graphic and text separation methodand a text enhancement method.

BACKGROUND OF THE INVENTION

Recently, multi-function peripheral device is popular for digital imageprocessing. It provides functions for image scanning and printing. InMulti-function peripheral device, graphic and text separation and textenhancement are often processed in Multi-function peripheral device.

Document usually comprises a graphic part and a text part. By way ofgraphic and text separation processing, the graphic part and the textpart can be separated for further processing. For example, in case ofwithout graphic/text separation process, when printing a document,printers use color ink to print the whole content. That is, the textpart will be printed with color ink as well and therefore wastes colorink. However, in case of having graphic and text separation process, thegraphic part is printed with color ink and the text part is printed withblack ink and therefore the color ink is saved.

The graphic and text separation methods of prior art comprise a hueadjusting method, an edge detecting method and a chroma and luminancedetecting method. These prior art methods do not classify the imageaccording to text and graphic, but apply a single process on the wholeimage. It won't provide a good graphic and text separation resultwithout classifying the image according to graphic and text. Forexample, the hue adjusting method adjusts the hue of the whole image,such as increasing the hue of the brighter part of the image andreducing the hue of the darker part of the image, to separate graphicand text. Because graphics and texts are subjected to the same processof hue adjusting, it will impact the hue of the whole image.

Besides, the edge enhancement method often incorrectly recognized thenoise and graphics of the image of document as texts and thereforegenerated error recognition result. However, applying the method whichused chroma and luminance to separate text and graphic on low or zerochroma photos will also fault the result.

The purpose of text enhancement is to make the image of text clearer.The prior art methods for text enhancement do not separate text andgraphic before the text enhancement process, but adjust the luminance ofthe whole image to clear the text image. However, such adjustment willdecrease the hue of the graphics of the document.

SUMMARY OF THE INVENTION

The first purse of the present invention is to provide a graphic andtext separation method which generates correct separation result bydividing a document image into plural image chips and determining thetype of each image chip.

The other purpose of the present invention is to provide a textenhancement method which generates good enhancement result by separatingthe graphic part and the text of the image first then enhancing the textpart.

According to the present invention, a graphic and text separationmethod, for separating a graphic part and a text part of an image,comprising: (a). coarse classification steps comprising: a1. dividingthe image into plural rows and dividing each of the rows into pluralchips, wherein each of the chip includes plural pixels; a2. classifyingthe plural chips into several chip types including photo chip, whitechip, black chip, screen chip, semi-screen chip and undefined chip; anda3. calculating the number of luminance transition of each chip todetermine if the chip is a transition chip or a text-on-photo chip; and(b). advanced classification steps, comprising: b1. determining if theundefined chips are text chips; b2. grouping the plural chips intoseveral blocks, wherein each block comprises J×K chips and assigningeach block as a photo block, background block or a non-photo blockaccording to the chip types included in the block; b3. modifying thetypes of chips of each block; and b4. determining if the non-photoblocks shall be modified into photo block according to the types of twoneighbor blocks; and (c). a step of detecting texts on photo,determining another block range with a center at one targettext-on-photo chip, wherein the another block range comprises L×M chips,and determining if the transition chips within the another block rangeshall be modified into text-on-photo chips or if the text-on-photo chipswithin the another block range shall be modified into photo chipsaccording to the number of text chips within the another block range.

In an embodiment, in the step a2, the determination of the chip types ismade according to chroma statistic, luminance statistic, boundarydetection and screen detection.

The chroma statistic comprising: classifying each pixel of each chipinto colorless pixel, mid-color pixel or colorful pixel, and determiningif the pixel is a photo pixel.

In an embodiment, the each pixel of the image is classified as colorlesspixel, mid-color pixel and colorful pixel according to the followingrules: set a matrix with the center at the pixel and calculate thechroma and luminance of the plural peripheral pixels around the centerpixel of the matrix, wherein the matrix is an M×M matrix; classifyingthe plural peripheral pixels into the colorless pixel, mid-color pixeland colorful pixel; and determining if the pixel is a photo pixelaccording to the numbers of mid-color pixel and colorful pixel of theplural peripheral pixels.

In an embodiment, a photo chip is determined according to the number ofphoto pixel.

In an embodiment, the luminance statistic comprising classifying thepixels of the image into a white pixel, a gray pixel or a black pixel.

In an embodiment, each pixel is classified as white pixel, gray pixel orblack pixel according to the following rules: set a matrix with thecenter at one target pixel and calculate the luminance of the pluralperipheral pixels around the center pixel of the matrix, wherein thematrix is an M×M matrix; classifying the plural peripheral pixels intowhite pixel, gray pixel and black pixel; and determining if the centerpixel is white pixel, gray pixel or black pixel according to the numbersof white pixel, gray pixel and black pixel of the plural peripheralpixels.

In an embodiment, a white chip is determined according to the number ofbackground pixel contained in the chip, a chip is photo chip isdetermined according to the number of gray pixel contained in the chipand a black chip is determined according to the number of black pixelcontained in the chip.

In an embodiment, the edge detection comprising calculating the edgevalues of each pixels of the image; determining if the pixel is aneffective edge according to the absolute value of the edge value;calculating the gradients of the pixels of effective edges; andclassifying the pixel with a gradient value larger than 0 as text pixeland the pixel with a gradient value smaller than 0 as white pixel.

In an embodiment, the step of determining a screen chip or a semi-screenchip is according to the number of screen pixel contained in the chip.

In an embodiment, a screen pixel is determined according to thefollowing rules: with the center at one target pixel, using a Laplaciangradient operator to determine if the peripheral pixels are located at ascreen area; determining if the target pixel is a screen pixel accordingto the number of pixels located at the screen area.

In an embodiment, the luminance transition calculation comprisingcalculating the number of luminance transition of each chip according tothe luminance distribution of the chip; determining the chip with atleast one luminance transition as a transition chip; and determining ifat least one of three neighbor pixels is a text-on-photo chip accordingto the number of luminance transition generated by the three neighborpixels, wherein when the transition number is within a value range andthe middle chip of the three neighbor chips is photo chip, the middlechip is determined as text-on-photo chip.

In an embodiment, the step b2 comprising determining a non-photo blockaccording to the number of screen chip and the number of photo chip ofthe block; determining a photo block according to the sum of the numberof photo chip and the number of screen chip and the number ofsemi-screen chip of the block; determining a photo block according tothe sum of the number of photo chip and the number of screen chip andthe number of black chip of the block; determining a photo blockaccording to the number of photo chip of the block; and determining abackground block according to the number of background chip of theblock.

In an embodiment, in the step b4, when at least one block of the twoblocks at two sides of a non-photo block is a photo block, modify thenon-photo block into a photo block; and modifying the screen chips andblack chips of a photo block into photo chip.

The present invention also discloses a text enhancement method, forenhancing the image of a text part of an image comprising a graphic partand the text part, comprising a. a step of separating the graphic partand the text part, comprising: dividing the image into plural rows anddividing each of the rows into plural chips; classifying the chips intophoto chips and text chips, wherein the text chips comprise white textchips and black text chips; b. a step of text enhancement comprising setthe luminance of the black text chips as 0 and set the luminance of thewhite text chips as 255.

In another embodiment of the present invention, a text enhancementmethod, for enhancing the image of a text part of an image comprising agraphic part and the text part, comprising a. a step of separating thegraphic part and the text part comprising dividing the image into pluralrows and dividing each of the rows into plural chips; classifying thechips into photo chips and text chips, wherein the text chips comprisewhite text chips and black text chips; b. a step of text enhancementcomprising applying an unsharp mask on the text chips to enhance thecontrast of the text chips.

The above objects and advantages of the present invention will becomemore readily apparent to those ordinarily skilled in the art afterreviewing the following detailed description and accompanying drawings,in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a document including graphic part and text part;

FIG. 2(A) illustrates a document divided into rows and chips;

FIG. 2(B) illustrates plural pixels of a chip;

FIG. 3 illustrates an M×M pixel matrix;

FIG. 4 illustrates luminance transition; and

FIG. 5 illustrates a serial of neighbor blocks.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Please refer to FIG. 1, it shows a document 10 composed of a graphicpart and a text part. As shown in FIG. 1, document 10 comprises agraphic part 100 and a text part 200. The graphic part 100 comprises aphoto and a text “WELCOME” on the photo. And the text part 200 isconstituted of many characters T.

The graphic and text separation method of the present invention is torecognize the graphic part 100 and the text part 200. And the textenhancement method of the present invention is to enhance the text part200 after the separation is completed to distinct the text part 200 andthe text “WELCOME” on the photo 100.

We'll describe details of the graphic and text separation method of thepresent invention below. Please refer to FIGS. 2A and 2B. As shown inFIG. 2A, the graphic and text separation method of the present inventiondivides the document image 10 into plural rows L1-Ln and each row isdivided into plural chips 300. As shown in FIG. 2B, each chip 300 isconstituted of plural pixels, and in FIG. 2B, we take N pixels P1 . . .PN as an example.

After the image of document 10 is divided into plural chips 300, wedetermine whether each chip belongs to the text part 200 or the graphicpart 100 according to several rules and therefore definitely separatethe graphic part 100 and the text part 200.

The graphic and text separation method of the present inventioncomprises tow parts: (1) coarse classification and (2) advancedclassification. The method will further comprise a text-on-photodetection step if required. The details will be described as below.

Coarse Classification

In the coarse classification, the method of the present inventionclassifies the chips of document 10 to photo chip, white chip, blackchip, undefined chip, screen chip and semi-screen chip according tochroma statistic, luminance statistic, boundary detection and screendetection. Besides, the method also uses transition detection to findtransition chip and text-on-photo chip.

(1). Chroma Statistic

Since the graphic part of document are usually colorful, we can usechroma to identify the graphic part. Chroma statistic comprisesgenerating chroma of pixels from the color difference a,b of pixels andclassifying the pixels into colorless pixel, mid-color pixel andcolorful pixel according to the luminance of pixels. Since thecalculating of chroma and luminance is well known by the skilled personof the art, no more details will be described here.

According to the chroma and luminance of each pixel, we can justifywhether the pixel is colorless pixel, mid-color pixel or colorful pixel.Please refer to the table below.

Luminance colorful mid-color colorless A1-A2 chroma ≧ B1 B1 > chroma ≧B2 chroma < B3 A2-A3 chroma ≧ B4 B4 > chroma ≧ B5 chroma < B6 A3-A4 . .. A4-A5 . . . A5-A6

For example, when the chroma of a pixel is larger than or equal to B1and the luminance of the pixel is between A1 and A2, the pixel isclassified as a colorful pixel. When the chroma of a pixel is smallerthan B1 and larger than b2, and the luminance of the pixel is between A1and A2, the pixel is classified as a mid-color pixel, and so forth.

In order to justify whether an image chip is photo chip, we have tojustify whether the pixels of the chip are photo pixels. Please refer toFIG. 3. In FIG. 3, we are going to justify if pixel P6 is a photo pixel.First, we have a matrix with the center at pixel P6 and calculatenumbers of colorless pixel, mid-color pixel and colorful pixel among theperipheral pixels around pixel P6 in the matrix. In FIG. 3, the matrixis an M×M matrix. According to the numbers of colorless pixel, mid-colorpixel and colorful pixel contained in the matrix, we can decide whetherthe pixel P6 is a photo pixel. For example, if the number of mid-colorpixel is larger than c1 or the number of colorful pixel is larger thanc2, the pixel P6 will be classified as a photo pixel.

According to the rules, we can obtain the number of photo pixel amongpixel P1-PN of chip 300 and according to the number of photo pixel todetermine if chip 300 is a photo chip. For example, when the number ofphoto pixel of chip 300 is larger than c3, chip 300 is classified asphoto chip.

(2). Luminance Statistic

Luminance statistic is used for classifying image chips into white chip(means the background image of document, also called background chip),gray chip and black chip.

The document image is classified into background, gray and blackaccording to luminance range. Please refer to the table below.

Classification Luminance Range Bright L1-L2 Gray L2-L3 Dark Gray L3-L4

Referring to the rules of Chroma Statistic, before we decide whether achip is background chip, gray chip or black chip, we have to decidewhether each pixel of the chip is background pixel, gray pixel or blackpixel.

As shown in FIG. 3, we define an M×M matrix with the center at pixel P6and classify the peripheral pixels of pixel P6 into background pixel,gray pixel and black pixel. The attribute of pixel P6 is determinedaccording to the numbers of background pixel, gray pixel and black pixelin the M×M matrix.

For example, when the number of bright pixel is larger than d1, thecentral pixel P6 is a background pixel. When the number of gray pixel islarger than d2, the central pixel P6 is a gray pixel. When the number ofdark gray pixel is larger than d3, the central pixel P6 is a black pixel

After the attribute of each pixel of each chip was determined, wedetermine the attribute of each chip according to the numbers ofbackground pixel, gray pixel and black pixel contained in each chip. Forexample, a chip having more than d4 background pixels is determined as abackground chip. A chip having more than d5 gray pixels is determined asa gray chip. A chip having more than d6 black pixels is determined as ablack chip. The background chip is usually the background of graphic andgenerally is white. Because the graphic of document usually has graytone, so gray chips are classified as photo chip. Besides, black chipmeans the image being close to black.

(3). Screen Detection

Luminance statistic can be used for identifying the screen area ofdocument image. In the present invention, in addition to the forgingchip attributes, we further use luminance statistic to define screenchip and semi-screen chip.

Regarding to document of print, the screen areas are usually coloredareas.

The screen chip and the semi-screen chip are determined according to thenumbers of screen pixel contained in each chip. For example, a chiphaving f1 screen pixels is identified as a screen chip. When the numberof screen pixel of a chip is larger than f2 but smaller than f1, thechip is identified as a semi-screen chip.

According to the following rules, pixels of each chip are justified as ascreen pixel or not:

Defining an M×M matrix with a center at one target pixel and applyingLaplacing gradient operator on the peripheral pixels around the centerpixel in the matrix to determine if the peripheral pixels locate in ascreen area;

Determining if the center pixel is a screen pixel according to thenumber of pixels in the screen area. If there are more than f4 pixels inthe screen area, the center pixel is a screen pixel.

These screen chips or semi-screen chips will be modified as photo chipsor text-on-photo chips.

(4). Boundary Detection

The purpose of edge or boundary detection is to find the edges of texts.In the present invention, the undefined chips which are not classifiedinto photo chips, background chips or gray chips may be the text part ofthe document.

Boundary detection comprises the following steps:

-   1. Calculating the edge value of each pixel.-   2. Determining if the pixel is a valid pixel according to the    absolute value of the edge value.

For example, if the edge value is larger than e1, the pixel is a validpixel. If not, the pixel is an invalid pixel.

-   3. Calculating the gradient of the valid edge.

If the gradient of the pixel is larger than 0, the pixel is alow-brightness edge. If the gradient of the pixel is smaller than 0, thepixel is a high-brightness edge.

-   4. Classifying the pixels with their gradients more than 0 as text    pixels, and the pixels with their gradient smaller than 0 as    background pixels.

It is noted that the calculations of edge value and gradient are wellknown by the skilled persons in the art, no more details will bedisclosed in the specification.

(5). Transition Detection

Transition detection is used to find the rapid luminance change in spaceor time axis, especially the change of suddenly becoming black or white.In the present invention, we'll calculate the numbers of transitions ofeach chip to determine which chips are transition chip or text-on-photochip.

Please refer to FIG. 4, it shows an example of the luminance transitionof a chip. FIG. 4 shows the luminance curve of all pixels of a chip anda rapid luminance change T of pixels (i.e. suddenly from high brightnessto low brightness, means the luminance difference between two neighborpixels is very large), and T is called a transition.

Transition detection comprises the following steps:

According to the distribution of luminance of each chip's pixels todetermine if the chip has a transition;

Set the chip with the transition as a transition chip; and

Determining if at least one of the a plural transition chips isdetermined as a text-on-photo chip. For example, we calculate the sum oftransition of three neighbor transition chips. If the sum of thetransition is larger than g1 and smaller than g2, we justify the middlechip of the transition chips as text-on-photo chip. The middle chip mustbe classified as photo chip or screen chip according to chroma statisticor as a screen chip according to screen detection. The chips without thementioned transition sum are still classified as transition chip.

Advanced Classification

According to the chroma statistic and luminance statistic, we classifythe chips of the document into 6 chip types including photo chip, whitechip, black chip, undefined chip, screen chip and semi-screen chip forthe advanced classification steps. In the advanced classification, thepurpose is to classify all chips into photo chip, white chip, black chipand text chip. After the advanced classification, all undefined chipswill be classified as text chip. Besides, after the advancedclassification, a step for detecting text-on-photo chip is performed.The transition chips and text-on-photo chips identified in the luminancetransition detection will be used to detect text-on-photo chips.

In the advanced classification, we first determine the types of theundefined chip and then combine plural chips as a block. We'll determinethe type of each block and classify the blocks into photo block,background block and non-photo block. In other words, in the advancedclassification, based on two-dimensional concept, according to the typesof neighbor chips, we precisely modify the types of chip obtained in thecoarse classification steps. Then we determine the type of a blockconstituted by plural chips. After the block type is determined, theundefined chips in the block are classified as the same type as theblock.

In the following, we'll describe the classification with the unit ofchip.

The photo type chips usually locate at graphic part of document, whitechips usually belong to background of document, black chips are theblack part of texts, and the undefined chips means the chips which cannot be classified into any specific types. Generally, the undefinedchips are possible the text part of document. However, the undefinedchips may be photo chips. So we need to verify in the advancedclassification if the undefined chips belong to text part.

Next, we'll describe the process of modifying chip types in the unit ofblock. We assume a block has J×K chips. The type of each block isdetermined according to the chip types contained in the block. The rulesare listed in the following table.

Possible Image Number of Chip Type in Each Block Type Block Type Numberof screen chip <= m1 and Text Non-photo Number of photo chip < m2 blockNumber of photo chip + Number of Photo Photo Block screen chip + Numberof semi-screen chip <= m3 Number of photo chip + Number of Photo PhotoBlock screen chip >= m4, and Number of block chip >= m5 Number of photochip >= m6 Photo Photo Block Number of background chip >= m7 BackgroundBackground Block

Each block is classified as non-photo block, photo block or backgroundblock according to the table. Then in each block, we modify the chipswhich may be photo chips (such as screen chip, semi-screen chip andblack chip) into photo chips, or modify the semi-screen chip intoun-define (text) chip. Next, we further use the correlation betweenneighbor blocks to modify block types.

As shown in FIG. 5, for the non-photo type block n, if the m neighborblocks at two next sides of block n are all photo blocks, the block nwill be modify into photo type block.

The screen chips and black chips in photo blocks are modified into photochips. Besides, after the advanced classification, the unmodifiedsemi-screen chips will be classified as un-define chips. If the pixelsof un-define chips have edge characteristic (according to the edgedetection step), the undefined chips will be classified as text chips.Besides, if the pixels concluded in a single undefined chip are allblack pixels or white pixels, the undefined chip will be classified astext chip.

After the advanced classification are completed, all undefined chips areclassified as text chips.

Step for Detecting Text-on-Photo

We can use the numbers of text-on-photo chips within another range ofblocks to detect texts printed on photo. The range is usually rectangle,that is, the horizontal distance is longer than the vertical distance.The determination of the block range usually relates to the size of thetarget text. (The size of target text means the pixel number of the textimage.) For example, when the number of text-on-photo chips of a blockis larger than a specific value, we determine the block being located attext part and we modify the transition chips in the block intotext-on-photo chips. And when the number of text-on-photo chips within ablock is smaller than the specific value, we modify the text-on-photochips into photo chips.

Text Enhancement

After the graphic and text separation process is completed, we can usethe separation result to perform the text enhancement. Because thephotos and texts have been classified into graphic part (photo chips),background part (white chips) and text part (black chips), we can easilyprocess the chips according to the types of chip to get good result oftext enhancement, but won't improperly change the hue of graphic part ofdocument. During the enhancement process, we won't process the photochips which represent the graphic part of document, but adjust theluminance of text chips (including the texts on background and the textson photo) to distinct the text part.

Text chips are classified into white text chip or black text chipaccording to the luminance of pixels of each chip. When a chip has N1pixels with their luminance larger than T1, the text chip is determinedas white text chip. When a chip has N2 pixels with their luminancesmaller than T1, the text chip is determined as black text chip. We canset the luminance of each black chip as 0 and set the luminance of eachwhite chip as 255. Thus, we make the black part blacker and the whitepart whiter. Another method is to apply unsharp mask process on the dataof each chip to increase the contrast of text chips.

While the invention has been described in terms of what is presentlyconsidered to be the most practical and preferred embodiments, it is tobe understood that the invention needs not be limited to the disclosedembodiment. On the contrary, it is intended to cover variousmodifications and similar arrangements included within the spirit andscope of the appended claims which are to be accorded with the broadestinterpretation so as to encompass all such modifications and similarstructures.

1. A graphic and text separation method, for separating a graphic partand a text part of an image, comprising: (a). coarse classificationsteps, comprising: a1. dividing the image into plural rows and dividingeach of the rows into plural chips, wherein each of the chip includesplural pixels; a2. classifying the plural chips into several chip typesincluding photo chip, white chip, black chip, screen chip, semi-screenchip and undefined chip; and a3. calculating the number of luminancetransition of each chip to determine if the chip is a transition chip ora text-on-photo chip; and (b). advanced classification steps,comprising: b1. determining if the undefined chips are text chips; b2.grouping the plural chips into several blocks, wherein each blockcomprises J×K chips and assigning each block as a photo block,background block or a non-photo block according to the chip typesincluded in the block; b3. modifying the types of chips of each block;and b4. determining if the non-photo blocks shall be modified into photoblock according to the types of two neighbor blocks; and (c). a step ofdetecting texts on photo determining another block range with a centerat one target text-on-photo chip, wherein the another block rangecomprises L×M chips, and determining if the transition chips within theanother block range shall be modified into text-on-photo chips or if thetext-on-photo chips within the another block range shall be modifiedinto photo chips according to the number of text chips within theanother block range.
 2. The graphic and text separation method accordingto claim 1, wherein in the step a2, the determination of the chip typesis made according to chroma statistic, luminance statistic, boundarydetection and screen detection.
 3. The graphic and text separationmethod according to claim 2, wherein the chroma statistic comprising:classifying each pixel of each chip into colorless pixel, mid-colorpixel or colorful pixel, and determining if the pixel is a photo pixel.4. The graphic and text separation method according to claim 3, whereineach pixel of the image is classified as colorless pixel, mid-colorpixel and colorful pixel according to the following rules: set a matrixwith the center at the pixel and calculate the chroma and luminance ofthe plural peripheral pixels around the center pixel of the matrix,wherein the matrix is an M×M matrix; classifying the plural peripheralpixels into the colorless pixel, mid-color pixel and colorful pixel; anddetermining if the pixel is a photo pixel according to the numbers ofmid-color pixel and colorful pixel of the plural peripheral pixels. 5.The graphic and text separation method according to claim 4, wherein aphoto chip is determined according to the number of photo pixel.
 6. Thegraphic and text separation method according to claim 5, wherein theluminance statistic comprising: classifying the pixels of the image intoa white pixel, a gray pixel or a black pixel.
 7. The graphic and textseparation method according to claim 6, wherein each pixel is classifiedas white pixel, gray pixel or black pixel according to the followingrules: set a matrix with the center at one target pixel and calculatethe luminance of the plural peripheral pixels around the center pixel ofthe matrix, wherein the matrix is an M×M matrix; classifying the pluralperipheral pixels into white pixel, gray pixel and black pixel; anddetermining if the center pixel is white pixel, gray pixel or blackpixel according to the numbers of white pixel, gray pixel and blackpixel of the plural peripheral pixels.
 8. The graphic and textseparation method according to claim 7, wherein a white chip isdetermined according to the number of background pixel contained in thechip, a chip is photo chip is determined according to the number of graypixel contained in the chip and a black chip is determined according tothe number of black pixel contained in the chip.
 9. The graphic and textseparation method according to claim 8, wherein the edge detectioncomprising: calculating the edge values of each pixels of the image;determining if the pixel is an effective edge according to the absolutevalue of the edge value; calculating the gradients of the pixels ofeffective edges; and classifying the pixel with a gradient value largerthan 0 as text pixel and the pixel with a gradient value smaller than 0as white pixel.
 10. The graphic and text separation method according toclaim 9, wherein the step of determining a screen chip or a semi-screenchip is according to the number of screen pixel contained in the chip.11. The graphic and text separation method according to claim 10, ascreen pixel is determined according to the following rules: with thecenter at one target pixel, using a Laplacian gradient operator todetermine if the peripheral pixels are located at a screen area;determining if the target pixel is a screen pixel according to thenumber of pixels located at the screen area.
 12. The graphic and textseparation method according to claim 11, wherein the luminancetransition calculation comprising: calculating the number of luminancetransition of each chip according to the luminance distribution of thechip; determining the chip with at least one luminance transition as atransition chip; and determining if at least one of three neighborpixels is a text-on-photo chip according to the number of luminancetransition generated by the three neighbor pixels, wherein when thetransition number is within a value range and the middle chip of thethree neighbor chips is photo chip, the middle chip is determined astext-on-photo chip.
 13. The graphic and text separation method accordingto claim 12, wherein the step b2 comprising: determining a non-photoblock according to the number of screen chip and the number of photochip of the block; determining a photo block according to the sum of thenumber of photo chip and the number of screen chip and the number ofsemi-screen chip of the block; determining a photo block according tothe sum of the number of photo chip and the number of screen chip andthe number of black chip of the block; determining a photo blockaccording to the number of photo chip of the block; and determining abackground block according to the number of background chip of theblock.
 14. The graphic and text separation method according to claim 13,wherein in the step b4, when at least one block of the two blocks at twosides of a non-photo block is a photo block, modify the non-photo blockinto a photo block; and modifying the screen chips and black chips of aphoto block into photo chip.